Conventional surfboards, used for riding waves, are formed of an elongated buoyant board having a smooth surface with a pointed bow and a generally straight transverse stern. The sportsman is forwardly propelled by the breaking waves while standing up or lying on his chest on the board.
One partially improved surfboard is shown in the international application laid open under the No. WO 90/03306 on Apr. 5, 1990 in the name of Marica ION. The ION application shows a surfboard having arcuate, frontwardly convex ridges on its underface. Each ridge has a hydrodynamic shape more particularly defining a rearwardly sloping front face and an inclined or upright rear face. The surfboard is destined to floatingly slide upon the water surface mainly by resting on the front surface of the ridges, while rearwardly oncoming water will hit the rear surface of the ridges to frontwardly drive the surfboard.
It has been found by the inventors that the directional stability and the propelling efficiency of conventional surfboards could be improved.